Allergens are the most abundant proteins of pollen and constitute the major cause of allergies in temperate regions.
Certain genetically predisposed individuals become hypersensitive (allergic) to antigens stemming from extremely varied environmental sources. Antigens capable of inducing an immediate or delayed hypersensitization reaction are referred to as allergens. Allergens can have as their origin notably trees, herbaceous plants, insects, mammals, food, drugs and chemical products. Allergens are classified in groups I to V according to their immunochemical properties. The allergen Dac g 5 of Dactylis glomerata belongs to group V as does the allergen Lol p V of Lolium perenne. 
The antibodies involved in allergy belong to the IgE class of immunoglobulins. In the presence of an allergen, IgE binds to mastocytes and basophils, which leads to the release by these cells of different chemical mediators and thus to the manifestation of allergy. Allergy can be manifested in different forms such as, e.g., anaphylactic shock, asthma, rhinitis or atopic dermatitis.
When the diagnosis of allergy to a particular compound has been established, desensitization of the patient in relation to the implicated allergen is the most frequent therapeutic approach, especially when the presence of the allergen cannot be avoided as in the case of pollen and acarids. This type of treatment has proven to be effective, but it requires the availability of an effective and safe product. In fact, the treatment presents a risk of anaphylactic shock such that the administered product must be free of any impurities that could constitute another potential allergen. At present, it is only known to use complex mixtures of allergens and not pure products. It is, therefore, necessary to have available allergens in a structural form as close as possible to the natural allergen and having the highest possible degree of purity.
One of the possible means for attaining this goal is the production of recombinant allergens in a host organism (Laffer, S. et al., J. Allergy Clin. Immunol., September 1996, volume 98, no. 3, pages 652-658).
As examples, we can cite the patent application published as No. 819 763 which describes the production of the modified allergen Der f II. The European patent published as No. 406 286 describes the cloning of a major allergen of rye grass pollen, Lol p 1, and the expression of this gene. The patent application published as No. 473 111 also discloses the production of recombinant acarid allergens used for desensitization. The patent application published as No. 463 059 pertains to allergens taken from ragweed and the use of these proteins. These applications disclose the expression of genes and the production of proteins in E. coli. 
This system of expression has the disadvantage of not enabling the post-translational modifications of the proteins which can be implemented in eukaryote cells. For example, the proteins produced are not glycosylated. However, the glycosylation of certain allergen proteins can be important for their ability to bind to IgE (Van Ree et al., J. Biol. Chem., 2000, volume 275, pages 11451-11458).